The present invention refers to a sample holder for positioning a sample in an electron microscope (EM), which is configured to perform transmission Kikuchi diffraction (TKD) measurements. Moreover, the present invention refers to an electron microscope (EM) comprising the sample holder according to the invention, wherein the EM is configured to perform transmission Kikuchi diffraction (TKD) measurements.
Electron backscatter diffraction (EBSD), which is also known as backscatter Kikuchi diffraction (BKD), is a well known technique of electron microscopes (EM) to measure crystal orientations. It is applicable to any crystalline material (in theory) and provides absolute crystal orientation with sub-micron spatial resolution. Moreover it is a useful tool for discriminating between phases.
Thereby backscattered electrons strike a phosphor screen of an EBSD detector and produce light, which is detected by a CCD (charge-coupled device) camera of the EBSD detector, digitised and sent to a computer. The biggest advantages of EBSD analysis are that a correlation between local texture and microstructure can be distinguished as well as a grain boundary and a grain size analysis can be done.
Signal yield and distribution are a function of working distance (WD), sample-screen distance (DD), acceleration voltage, sample tilt and the density of the material. The working distance is the length the electron beam travels inside the SEM chamber, i.e. between the sample and the surface of a column (comprising the electron lenses of the EM) which is closest to the sample, especially between a pole piece (of an electron lens) of the EM and the surface of a sample. The sample-screen distance is the distance between the sample (point source) and the phosphor screen. An in-situ screen positioning provides high flexibility in WD and DD whereby the EBSD signal can be optimized for each measurement.
Nowadays EBSD detectors of EMs have also been used to perform measurements with a technique that is called transmission Kikuchi diffraction (TKD), also known as transmission electron backscatter diffraction (t-EBSD). To perform TKD measurements, samples are prepared as for transmission electron microscopy (TEM). Thus the samples are electron transparent. The samples are mounted to be horizontal or tilted by slight a negative angle (e.g. 10 to 20 degrees) from the horizontal that is in the opposite way round as known for EBSD. The sample is positioned above the phosphor screen of the EBSD detector. Therefore the electron beam hits the upper side of the sample and transmitted electrons are detected by the EBSD detector. Thus a diffraction pattern from the lower surface (exit surface) of the electron transparent sample is obtained. Investigations proved that TKD improves the lateral spatial resolution by an order of magnitude compared to EBSD.
Up till now sample holders for TKD have been improvisational and are disadvantageous in terms of handling thin (very fragile) samples and have a negative influence on the quality of measurements.
One known way of fixing a sample or a sample carrier inside an EM is to adhere it to a sample stub. This way of fixing is relatively time consuming and intensifies the C contamination phenomenon which is detrimental to the measurements. Moreover the sample cannot be subsequently separated from the stub without being damaged.
Another known possibility to fix the sample is described in "
JPS6148647U discloses a sample holder according to the preamble of claim 1.
J Further sample holders are disclosed in
The intention of this invention is therefore to provide a sample holder and an electron microscope that feature improved sample handling capabilities and signal quality.
In order to solve the above mentioned technical problem, there is provided a sample holder according to claim 1, and an electron microscope according to claim 7.
The sample holder, which is configured to perform Kikuchi diffraction (TKD) measurements, comprises a tip portion and is configured to fix a sample or a sample carrier comprising the sample in a form-locking and/or a force-locking manner at or in the tip portion.
Further, the sample holder comprises a movable or rotatable element, configured to fix the sample or the sample carrier. The sample holder is configured to provide a snap action of the movable or rotatable element between a loading position and a closed position, such that a portion of the rotatable element is slidable along the elastic element, wherein a surface of the portion has a greater radius to an axis of the rotatable element than at least one surface of the rotatable element adjacent to the portion.
As the sample holder comprises a tip portion and the sample or the sample carrier (at which a sample can be arranged) are fitted at or in the tip portion, a practicable solution to fix the sample or the sample carrier at the sample holder was found without risking an unacceptable amount of shadowing, especially when the sample or the sample carrier is positioned at a (very) front end of the tip portion. Preferably the EM is a scanning electron microscope (SEM).
Preferably, a maximum cross-section dimension (diameter) at the (very) front end of the tip portion is less than 15 mm, more preferably less than 10 mm, especially less than 8 mm. This enables a very slim front end of the tip portion, which further enhances usability and quality of measurements.
The sample or the sample carrier are configured to perform TKD measurements and thus are at least partly electron transparent. Therefore they can be prepared as for a use in a transmission electron microscope (TEM). The sample or the sample carrier can have a shape, which is at least partially circular, with a diameter of approximately 3 mm (standard size for TEM grids). In other words, the sample or the sample carrier may have at least at an edge area of the sample or the sample carrier partly the shape of a disc.
Preferably, the tip portion of the sample holder has a cut-out, which extends from a front end of the tip portion backwards. Thereby an opening of the sample holder, which enables the sample (which can be on the sample carrier) to be accessible to an electron beam of the EM and detection of transmitted electrons, extends to the front end of the tip portion. Thus the tip portion does not cover the sample or the sample carrier at the front end of the tip portion. Due to this "open design" combined TKD and EDS (energy dispersive X-ray spectroscopy) measurements are possible, because the tip portion is not positioned between the sample and an EDS detector or an EBSD detector.
Preferably, the sample holder comprises a connecting member, more preferably a pin stub, which is configured for being connected to a stage of the EM. This makes the sample holder compatible to stages of EMs.
More preferably, the sample holder comprises a pin stub, which is configured for being stuck into a stage of the EM, and the sample holder has a contact plane, which is configured to receive the sample or the sample carrier, wherein an angle between a centre axis of the pin stub and the contact plane is greater than 90 ° and less than 180 °. This enables to compensate a tilt-angle of a tilted stage of the EM. By tilting the stage, a collision between the stage and a detector of the EM is prevented.
Preferably, the tip portion of the sample holder has a tapered shape. This enables a main body of the sample holder to be relatively massive compared to its relatively slim tip portion. Thus, the main body can have a user-friendly shape while preventing shadowing due to its relatively slim tip portion. More preferably, the tapered shape is located at a side of the tip portion facing away from the connecting member. This enables to reduce a minimum working distance between the sample and the surface of a column (comprising the electron lenses of the EM) of the EM which is closest to the sample. This surface may be provided by a pole piece of an electrode lens of the EM. The reduced minimum working distance improves a resolution of the EM. More preferably, the sample holder is configured to enable a minimum working distance of less than 5 mm, preferably less than 4 mm, more preferably less than 3.5 mm. A preferred working distance is between 6 and 3 mm. According to another preferred embodiment, the tapered shape is located at a side of the tip portion where the connecting member is arranged. This prevents shadowing of an EBSD detector of the EM.
According to another embodiment of the invention, the sample holder comprises a seat, which is configured to hold the sample or the sample carrier in all but one translational directions in the form-locking manner. The seat can comprise or be a recess that extends from a surface of the tip portion (preferably from a top surface of the tip portion) into the sample holder. Due to the seat, the sample or the sample carrier can be placed at or inside the sample holder without a risk of sliding of the sample holder.
Preferably, the seat has a shape, such that a circular sample or a circular sample holder protrudes from the tip portion at a front end of the tip portion. In other words, a sample or sample holder, which may be formed like a disc (at least at its edge area along its circumference) is fixed inside the seat such that a portion of its circumference extends out of the tip portion. This results in a minimized amount of shadowing in a space between an area of emitted x-rays (that emit from a surface of the sample facing an electrode lens of the EM) and an area of transmitted electrons (that transmit through the sample and emit from the surface that faces away from the electrode lens).
Preferably, the movable or rotatable element is configured to clamp the sample or the sample carrier. This prevents any movement of the sample or the sample carrier relative to the sample holder in a form-locking and/or force-locking manner. The rotatable element can be a hinged lever. Preferably the movable or rotatable element is configured to cover the sample or the sample carrier at a side that faces away from the front end of the tip portion only. Thus it does not cover neither the area of interest on the sample (usually the center of the sample or the sample carrier) nor the area at the sample or sample carrier front end. This prevents shadowing while performing combined TKD and EDS measurements.
According to a preferred embodiment, the movable or rotatable element is configured to fix the sample or the sample carrier in the remaining translational direction, which is not fixed by the seat. Therefore the sample or the sample carrier is fixed in all directions. Preferably the element fixes the sample or the sample carrier in a form-locking manner. Preferably the element is configured to press the sample into the seat. This eliminates possible play between the sample or the sample holder and the seat.
Preferably, the sample holder comprises an elastic element, preferably a spring, configured to actuate the movable or rotatable element. Thereby an embodiment was found, which can be handled easily and without using a screw.
Since the sample holder is configured to provide a snap action of the movable or rotatable element between a loading position and a closed position, the movable or rotatable element comprises two energetic stable positions, wherein the loading position enables the sample holder to receive the sample or the sample holder at its predetermined position. When the movable or rotatable element is in the closed position, the sample or the sample carrier is locked in or on the sample holder. Between these two positions the movable or rotatable element performs a snap action, which means, that if the movable or rotatable element is closed to a certain amount, it closes itself completely until the closed position is reached. If the movable or rotatable element is opened to a certain amount, it can open itself completely until the loading position is reached.
When the rotatable element is rotated, a snap action is created when the portion glides along the elastic element. When the sample holder is in a closed position and the elastic element still pushes the lever via the portion, the lever is pressed toward a stop (which can be the sample or the sample holder).
Moreover an electron microscope (EM) comprising the sample holder of any one of the previous claims is provided, wherein the EM is configured to perform transmission Kikuchi diffraction (TKD) measurements. Preferably the electron microscope is a scanning electron microscope (SEM). The EM and the SEM are characterised by their enhanced usability and their enhanced quality of measurements. The enhanced quality of measurements is realized by a maximized signal quality due to an optimum sample-detector geometry. A spatial resolution in TKD mode is improved by an order of magnitude compared to (conventional) EBSD.
Preferably, the EM comprises an EBSD (electron backscatter diffraction) detector, an EDS (energy dispersive X-ray spectroscopy) detector and/or an imaging detector, wherein the EM is configured to perform EDS measurements with the EDS detector, and/or to take images with the imaging detector in the same configuration as TKD measurements are performed with the EBSD detector. Thus the positions of the sample, the EBSD detector, the EDS detector and/or the imaging detector do not have to be changed (to do the above mentioned).
More preferably, the imaging detector is an in-column imaging detector. The imaging detector inside the column of the EM enables high magnified images. More precisely, the in-column imaging detector may be arranged inside a pole piece of an electron lens and/or between electron lenses of the column. In-column imaging detectors use secondary electrons (SE) and therefore may me named in-column SE detectors. Another known term would be in-lens SE detector. In-column detectors provide best imaging resolution, which is important for TKD measurements. To use the in-column detector the sample should to be close enough to the pole piece, e.g. at a working distance (WD) of 6 to 3 mm, which is possible due to the sample holder according to the invention.
Further aspects of the invention can be learned from the claims and the description.
The sample 12 and the sample carrier 13 are configured to perform TKD. They may be prepared as for a use in a transmission electron microscope (TEM) and thus may be at least partly electron transparent. Normally the sample 12 or the sample carrier has an at least partially circular (disc-like) shape with a diameter of approximately 3 mm.
The sample holder 10 comprises a tip portion 14 and is configured to fix the sample 12 or the sample carrier in a form-locking and/or force-locking manner at or in the tip portion 14. The sample holder 10 may comprise a seat 16, which may form a contact plane 18 to receive the sample 12 or the sample carrier 13. The seat 16 is configured to hold the sample 12 or the sample carrier 13 in all but one translational directions in a form-locking manner. As shown in
Moreover the sample holder 10 comprises a movable or (as shown in the example) a rotatable element 22, which may be a hinged lever, and is configured to fix the sample 12 or the sample carrier 13. The rotatable element 22 may be mounted as to rotate around an axis 23 of the sample holder 10, which is mounted in the main body 20. The element 22 may be configured to fix the sample 12 or the sample carrier 13 in the remaining translational direction. Moreover the element 22 may clamp the sample 12 or the sample carrier 13, such that a play is eliminated.
The tip portion 14 may have a cut-out 24 that extends from a front end 15 of the tip portion 14 backwards, such that the sample 12 or the sample carrier 13 is covered only at its edge areas 25 that are laterally and backwardly directed, when the movable or rotatable element 22 is in the closed position.
The sample holder 10 may comprise a handle 26, which is connected to element 22 and enables to open or to close the element 22 more easily.
The main body 20 may be connected to a connecting member 28 of the sample holder 10. The main body 20 and the connecting member 28 may be connected by a screw 30. The connecting member 28 is configured for being connected to a stage of an EM. Moreover, the connecting member 28 may be or comprise a pin stub 29, which may be stuck into the stage.
In
The sample holder 10 is configured to provide a snap action of the movable or rotatable element 22 between a loading position (according to
An angle between a centre axis 46 of the pin stub 29 and the contact plane 18 may be greater than 90° and less than 180°. In other words a contact plane 48, which is configured to rest on the stage of the EM, is tilted away from the contact plane 18. The sample holder preferably has an angle between the centre axis 46 of the pin stub 29 and the contact plane 18 (a pre-tilt) of 135°. For some SEMs with very small airlocks it might be necessary to reduce the angle so that they can go through such small airlocks.
The tip portion 14 of the sample holder 10 may have a tapered shape 44. The tapered shape 44 enables the sample holder 10 to be relatively slim at its front end of the tip portion 14. The tapered shape 44 at the side facing the pin stub (at the side below the sample 12 or the sample carrier 13 / at the same side with the transmitted signal) reduces shadowing while performing TKD measurements, while the tapered shape 44 at the side that faces away from the pin stub (at the top part) enables reducing a working distance (WD) between the sample 12 and the surface of a column 63 (comprising electron lenses 61 of the EM) which is closest to the sample 12. In the example shown in
The seat 16 fixes the sample 12 or the sample carrier 13 in a form-locking manner in all but one directions. In
Due to the angle between the centre axis 46 and the contact plane 18 of the sample holder 10, the contact plane 18 may be horizontally or tilted away from the EBSD detector 64. As the sample holder 10 is positioned at the side of the phosphor screen 65, which is closer to the pole piece 62 (the upper side of the phosphor screen 65), an angle between the surface of the phosphor screen 65 and the contact plane 18 is less than 90 °. This means that the surface of the sample 12 or the sample holder 13 facing away from the pole piece 62 is turned towards the EBSD detector 64.
The EM 60 is configured to perform EDS measurements with the EDS detector, and/or to take images with the imaging detector 67 in the same configuration as TKD measurements are performed.
The function of the sample holder 10 and the electron microscope 60 will be described below:
To fix the sample 12 or the sample carrier 13 inside the sample holder 10, the element 22 is turned towards the seat 16. This may be done by actuating the handle 26. While the element 22 is in a loading position (according to
Inside the EM 60, the sample holder 10 is arranged such that the sample 12 or the sample carrier 13 are in an as short as possible distance to the pole piece 62 (e.g. 3 mm), which is supported by the tapered shape 44 of the tip portion 14. The tapered shape 44 facing the EBSD detector 64 reduces shadowing while performing TKD measurements.
The sample 12 or the sample carrier 13, the column 63 comprising the electron lenses 61 with the pole piece 62, the EBSD detector 64, the EDS detector 68 and/or the imaging detector 67 may be arranged in a way, such that TKD measurements and EDS measurements can be made without changing the position of the sample holder 10, the column 63 comprising the electron lenses 61 with the pole piece 62, the EBSD detector 64 or the EDS detector 68. Moreover the parts of the EM 60 as mentioned above may be arranged such that the imaging detector 67, which may be arranged in the column 63 (comprising the pole piece 62) of the EM 60, can take images without the mentioned parts being moved. Thus all additional measurements can be done and images can be taken in the same configuration as TKD measurements are performed thanks to the design of the sample holder 10.
The sample holder 10 according to the invention enables to position a very thin and fragile sample 12 at a distance as short as possible from the pole piece 62 of the EM 60, wherein EDS and TKD measurements can be performed under optimal circumstances. The design of the sample holder 10 enables to perform EDS and TKD measurements simultaneously at a relatively short working distance from the pole piece 62 of the EM 60. Moreover, it enables a measurement-geometry that prevents shadowing at the phosphor screen 65 of the EBSD detector (EBSD camera) 64 to a minimum. Moreover, the sample holder 10 enables a comfortable fixation and a perfect protection of the sample 12 or the sample carrier 13.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.